In the context of post-marketing surveillance supporting public-health authorities to take evidence-based decisions to fight the spread of poor-quality medicines, the quality of antimalarial artemether-lumefantrine (AL) medicines was assessed in the Democratic Republic of the Congo (DRC). A total of 150 samples of AL-containing products was collected from private pharmaceutical outlets in 8 main cities: Goma, Kikwit, Kinshasa, Kisangani, Lubumbashi, Matadi, Mbandaka, and Mbuji-Mayi. All drug samples were successively analyzed by visual inspection, thin-layer chromatography (TLC), and high-performance liquid chromatography (HPLC) following The International Pharmacopoeia. Of the 150 collected drug samples, 3 (2%) failed the visual inspection as they had shelf lives different from those of other samples with the same brand name. Four samples (2.7%) did not pass the TLC test as they contained only 1 or even none of the 2 declared active pharmaceutical ingredients (APIs). HPLC assays showed that 46 (30.7%) samples had artemether contents below 90% and 17 (11.3%) above 110% of the content claimed on the label. For lumefantrine, 32 (21.7%) samples had contents below 90%, and 8 (5.3%) had contents above 110%. This survey in DRC gives evidence that poor-quality antimalarial medicines are widely present. Based on 3 detection techniques, the study shows the necessity to equip developing countries with modern techniques such as HPLC, which, if combined with affordable techniques like TLC, could provide a pertinent analytical strategy to combat drug counterfeiting and poor manufacturing.